Sheet material inspection apparatus



June 27, 1967 Filed May 29, 1964 D. A. LESLIE ET AL SHEET MATERIAL INSPECTION APPARATUS 5 Sheds-Sheet 1 I I 219' I/7 I L8 l /7 29 I n I I 24 25 S g 25 4 I 2/\, I J 23 2/ I n l 34 I i I 1 I H I! |"H I] |'/8 30 /8 I /6 4/ 20 20! 4/ /6 I I l -L7: 3:1- l I 3/ l /9 2; 99

I I I I 'm I L III" 1 III l2 INVENTORS DOUGLAS A. LESLIE PAUL NASH B YM ATTORNEYS.

June 27, 1967 D. A. LESLIE ET AL 3,327,398

SHEET MATERIAL INSPECTION APPARATUS Filed May 29, 1964 3 Sheets-Sheet z:

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Fl 4 1 I L] INVENTORS DOUGLAS A. LESLIE PAUL NASH ATTORNEYS.

June 27, 1967 D LESUE ET AL 332L398 SHEET MATERIAL INSPECTION APPARATUS Filed May 29, 1964 3 Sheets-Sheet 5 ROLLER MOTION AMPLIFIER SIGNAL CAUSED BY ROLLER MOTION NECESSARY) PAPER PAPER MOTION CUTTING MEANS ALARM MEANS SIGNAL USEFUL TO EFFECT SEPARATION OF REJECTS REJECTS RECORDER SIGNAL v SHEET ALARM PRODUCT SIGNAL INVENTORS,

DOUGLAS A. LESLIE,

PAUL NASH United States Patent 3,327,398 SHEET MATERIAL INSPECTION APPARATUS Douglas A. Leslie, Canada Glazed Papers Limited, 2131 Lawrence Ave. E., Scarborough, Ontario, Canada, and Paul Nash, 1355 Wellington St., Ottawa, ()ntario, Canada Filed May 29, 1964, Ser. No. 433,835 1 Claims priority, application Canada, May 30, 1963, 876,880 (Filed under Rule 47(2) and 35 U.S.C. 116) 17 Claims. (Cl. 3314S) This invention relates to a device for detecting areas of increased thickness on a web of moving sheet material, and particularly relates to a paper inspecting device for detecting wrinkles or bumps on a moving sheet of high quality paper material.

Normal slight variations in the thickness or smoothness of sheet material are usually not objectionable, and the present invention is concerned with the detection of undesirable defects in the form of bumps, lumps, calender cuts, wrinkles, or other areas of abruptly increased thickness referred to herein simply as defects or areas of abruptly increased thickness. Such defects occurring in sheet material such as paper, particularly coated paper, render the product inferior for certain uses and may indeed cause damage to printing presses to which the paper may eventually be subjected. These defects may be caused by the presence of colour lumps, or other foreign material present on the sheet material, or by the uneven distribution of moisture throughout the sheet material or may be due to a wrinkle or fold in the sheet material. Such a defect must be detected and those portions of the sheet material containing such defects must be removed in the production of high quality sheet material.

Prior methods for detecting such defects have included the visual inspection of sheets, however, this method is time consuming and is not of uniform accuracy.

Other prior proposals for detecting such undesirable defects in sheet material have included mechanical sensing members which ride on a moving web of sheet material in yielding contact therewith, and which are adapted to record or otherwise indicate thickness variation. For example, various devices have been proposed which include a pair of members through which the sheet material is passed, at least one of such members being yieldingly mounted and normally urged against the moving sheet material so that upon contacting an area of increased thickness, said member, by means of associated actuation devices, transforms the resultant mechanical impact to an electrical impulse which is transmitted to a recording, alarm, or other control system. However, such prior proposals made use of a stylus, flange member, or other relatively cumbersome mechanical detecting means mounted in stiff mechanical bearings or springs, resulting in relatively low sensitivity and inability to detect defects of a small area or of a small thickness, and hence were not suitable for the production of high quality sheet material products. Such detecting devices employing mechanically mounted sensing members were often subject to breakdowns or failure and were not liable to give consistent and accurate detection over a long period of time.

Many of the prior proposals also suffered from a disadvantage whereby the surface of the sheet material being tested was scratched or blemished by flange sensing members. These flange members or fingers which rode over the moving sheet material surface also frequently collected dirt and other waste material at the location of contact with the sheet material with the result that the surface of the sheet material was further scratched or otherwise marred. Such results are particularly undesirable 3,327,398 Patented June 27, 1967 in glazed or coated paper sheet surfaces which scratch or mar more easily, and which usually must be of a high quality finish.

The present invention attempts to overcome the above disadvantages by providing a device for detecting areas of abruptly increased thickness in a web of moving sheet material by the use of a roller, or a plurality of rollers, freely rotatable by the moving sheet material and urged thereagainst in rotating yield contact by air pressure means. When a roller contacts a defect or area of abruptly increased thickness on the sheet material, it is forced away from the sheet material. A secondary sensing means is provided which is actuated when :a roller moves away from the sheet material upon contacting an area of abruptly increased thickness, and is adapted to transmit a signal to associated alarm means. The rollers and air may be considered as comprising a primary sensing means or system. The rollers are preferably arranged in a housing or housings secured above the moving sheet material and the forced air may be directed into said housings towards and around the rotating rollers.

The present invention is particularly useful in detecting wrinkles or bumps and the like on a moving sheet of paper, especially coated paper, and a preferred embodiment includes a roller, or a series of rollers, arranged in an inverted U-shaped housing or housings across the width of the moving sheet of sheet material and having air directed through inlets in the upper housing towards the rollers so as to normally urge said rollers into rotating and yielding contact with the moving sheet material. The forced air also serves to lubricate the rollers as they rotate and avoids the necessity of employing relatively cumbersome mechanical mountings or bearings for said rollers. The rollers are preferably vertically movable on contacting a wrinkle or bump on the moving sheet material and such vertical movement actuates the secondary sensing means.

The secondary sensing means is dependent upon the relative position of the rollers and housing and includes any suitable system which will be actuated when the roller moves away from the moving sheet material upon contacting an area of abruptly increased thickness, and transmits an appropriate signal to associated alarm means. The secondary sensing means for example, may consist of a mechanical contact device, such as a spring or pointer, arranged within the housing and adapted to be contacted by a roller when it moves away from the sheet material. The said contact may be associated with known conversion means for translating the mechanical impulse received when the contact is actuated by a roller into an electrical signal which is transmitted by known means to the alarm system which is adapted to indicate those portions of moving sheet material having undesirable areas of abruptly increased thickness.

The secondary sensing means may also be based upon the air pressure variation caused when a roller moves further into the housing upon contacting a defect in the sheet material. In the embodiment of the invention utilizing inverted U-shaped housings with forced air entering through the upper portions of the housings, it will be appreciated that as a roller moves upwardly into the housing there will be a corresponding variation in air pressure or back pressure, which variations can be picked up by suitable sensing devices and converted into electrical signals.

A preferred form of the secondary sensing means comprises a light source shining on the point of contact of the rollers and the moving sheet material and a photoelectric cell on the other side of the roller normally substantially hidden from said light source but which is actuated when a roller moves vertically upon contacting a 9 t2 defect enabling light from the light source to shine through onto the photoelectric cell. The impulse received from the photoelectric cell may then be transmitted to an associated alarm means which may comprise an amplifying system and recording device, as Well as a control system which will automatically remove or otherwise indicate that portion of the moving sheet having a wrinkle, bump or other defect in excess of a predetermined minimum size.

The secondary sensing means or system may alternately comprise an electrical condenser or capacitor system wherein at least part of the housing forms at least one plate of the capacitor and wherein the roller is adapted to displace part of the (ii-electric material thus varying the capacitance of the capacitor and causing a signal to be transmitted to the alarm means. The air space within the housing will comprise at least part of the insulating or di-electric material and one plate of the capacitor may be in the housing with the other plate in a roller located on the opposite side of the moving sheet material, or both capacitor plates may be located in the housing. When a roller moves into the housing air space upon contacting a defect in the sheet material, the characteristics of the dielectric material are thus varied causing variations in the capacitance of the capacitor which in turn results in corresponding variations in the electric charge or current which may be passed on through known amplifying systems to the associated alarm means. A preferred arrangement is to provide a capacitor plate in each side of an inverted U-shaped housing, the plates being separated from each other and imbedded in an insulating material. The said insulating material together with the air space Within the housing acts as the dielectric material of the capacitor.

The rollers are normally urged against the moving sheet of material by the air pressure when the inspecting device is in operation. However, when it is desired to stop the operation of the detecting device, then it is necessary to provide a retaining means which will hold the rollers away from the moving sheet material, and such retaining means may be in the form of electromagnets, for example, arranged in the housing above the rollers. When it is desired to stop the operation of the inspecting machine it is preferable that the air pressure means he turned OE and the electromagnets simultaneously energized, thus lifting the rollers against the roof of their housings and retaining them there away from the moving sheet material.

The detecting apparatus of the present invention is particularly useful in association with paper or other sheet material handling machines which cut a roll or paper into sheets of a predetermined size. The detecting device may be mounted over the moving sheet of paper prior to its entry into the cutting portion of the machine and upon detecting a defect, the alarm means is adapted to actuate a mechanism in the cutting portion of the machine which will reject those sheets containing wrinkles, bumps, or other undesirable defects or at least separate them from those sheets that have no undesirable defects. Further grading means may be employed so as to separate the sheets into various separate piles depending upon the amount of defects contained thereon. The function of the alarm means is to receive signals or appropriate impulses from the secondary sensing means and to indicate to the operators of the device those portions of the sheet material having undesirable defects. This may be accomplished by audible alarm and/ or the position of the defects on the sheet material may be recorded by known means. The alarm means may also be adapted to control the quality of the sheet material and effect separation of portions of the sheet material containing undesirable defects. When a plurality of rollers are used, the alarm means can also be arranged to indicate the exact location of the undesirable defect or bump on the sheet material, since only that roller contacting the bump will actuate the alarm system, thus allowing the separation or other treat- 4- ment of that portion of the sheet material containing the bump.

The detection device of the invention may also be used in association with related paper inspecting devices which make use of variations in reflected or transmitted light such as blemish testers, colour detectors, refractometers or other known paper testing machines. Such known associated paper testing devices may be so arranged with the detection device of the present invention so as to employ a common secondary sensing and alarm system. The light source may, for example, be common to both the detecting device of the invention and the blemish testing device.

The present invention will be more clearly understood by reference to the following detailed specification read in conjunction with the accompanying drawings which illustrate a preferred form of the invention, and wherein:

FIGURE 1 is a vertical transverse sectional view of the detecting device;

FIGURE 2 is a top plan view of a portion of the detecting device;

FIGURE 3 is a front elevational view of a portion of the detecting device;

FIGURE 4 is a circuit diagram of electromagnet and air control system;

FIGURE 5 is a schematic diagram showing the general relationship between the signal produced by the detecting device and alarm means; and

FIGURE 6 is a cross sectional view of a detail of the detecting device.

Referring to the drawings, a sheet material 10 is illustrated moving in the direction of the arrowover roller 12 which revolves in a counter-clockwise direction. Defect detecting roller 14 is housed within an inverted U- shaped housing 16. Forced air is supplied from an air supply line 17 to individual air hose lines 18 downwardly through openings 19 in the roof of housing 16. Shallow troughs 20 are formed in the upper roof of housing 16 surrounding the air supply openings 19 and are so shaped as to deflect the air from hose lines 18 over a greater area of roller 14.

Housing 16 is supported by a plate 22 which is secured by means of retaining screws 23 onto support 24. Levelling screws 25 and adjusting screws 21 are provided to adjust the position of plate 22 relative to support 24. A spring 26 is provided on retaining screws 23 to normally urge plate 22 in its downward position which is fixed so that the lower portion 27 of housing 16 rests a short distance above moving sheet material 10 so that roller14 can easily engage the surface of the moving sheet material 10 and be vertically movable within housing 16. The spring 26 also serves as a safety device in the event that an overly large thickness or wad of material should be found on moving sheet material 10 and in such a case the roller 14, housing 16 and plate 22 would be forced upwardly against spring 26. The plate 22 should therefore be sufiiciently rigidly positioned so as toresist vertical movement when sheet material 10 containing normal size defects or wrinkles passes under roller 14, but will move upwardly against spring 26 in the event of an unduly large wad of foreign material or folded paper contained on moving sheet 10 passing under roller 14 and housing 16 so as to avoid damage to the equipment. Support 24 is hinged on mounting 28 which extends over sheet material 10 and is fixed to the fioor or machine structure (not shown). When the detecting device is not in operation, support 24 may be pivoted about point 29 by hinge means (not shown) thus raising plate 22 and housing 16.

Interlock switches 39 (FIGURE 4) may be located at the ends of support 24 and connected to an electrical circuit running through a D.C. converter to electromagnets 30 and operatively connected to an air control solenoid 40 associated through known valve means with the air supply line 17. FIGURE 4 shows a circuit diagram for such an arrangement and when support 24 is pivoted upwardly the interlock switches 39 are automatically thrown to a position closing the circuit thus actuating the air control solenoids 40 and an associated valve means to terminate the air pressure in the air supply line 17. At the same time, electromagnets 30 are energized and the magnetic poles 31 attract rollers 14 and retain them against the upper inner surface of housings 16 and away from the moving sheet material 10. The electromagnets also serve to prevent the rollers 14 from falling out of housings 16 when the detector head is raised upwardly.

Preferably more than one electromagnet 30 is evenly spaced over the length of roller 14 as illustrated in FIG- URES 2 and 3 so as to distribute the magnetic influence thereof over a greater portion of roller 14 and to provide the necessary balance and strength in lifting and retaining the roller within housing 16. The electromagnets 30 may be connected at one end to each other by wire 32 and connected to an A.C. or D.C. power source by lead lines 33, and connected at the other end by flux linking bar 34.

A light source 35 is positioned on one side of the housing 16 above sheet so that light shines towards the point of contact between the roller 14 and moving sheet material 10. When an area of suddenly increased thickness, wrinkle or bump passes under roller 14, said roller is momentarily raised upwardly at the point of the defect, allowing light from light source 35 to shine through and be received in photoelectric cell 37 (see FIGURE 1). Photoelectric cell 37 may be connected to known electrical amplifying circuits so that the variations in light intensity received in the photoelectric cell may be amplified and fed into a computer device or the like and a control system which will actuate an alarm system when the amplified signal reaches a predetermined intensity. The sensitivity of the detecing device may thus be varied by adjusting the amplifier according to the size of wrinkles or bumps it is desired to detect and it is possible to detect defects down to a size /2 mil in thickness or A in diameter or smaller by the present invention.

The general arrangement of the alarm means is shown schematically in FIGURE 5. The si nal produced by roller motion, amplified as necessary or desired, may be used to provide a record of the thickness of the sheet stock, to provide an alarm in case the roller motion exceeds certain pre-set limits, and to regulate production of the paper, all as is Well known per se in the art. That is, the signal, once generated, can be used in known ways to either indicate faulty production or to control production, as, for example, by separating defective material from out sheets of paper produced.

It is preferable to use a plurality of individual rollers 14 which are arranged across the width of the sheet of moving material, as indicated in FIGURES 2 and 3, and each roller should be of a convenient length so as to be able to easily move vertically or at least away from the sheet material upon contacting a defect thereon. Each roller 14 may be fitted into a separate housing 16, or a plurality of rollers can be arranged in a single housing with the number of rollers per housing or the length of a housing being dependent to some extent upon the air pressure to be used. The rollers are preferably formed of a relatively heavy and durable metal or metal alloy, and can be in the order of A or A of an inch in diameter when dealing With paper sheet material.

Separators 41 may be made of any suitable resilient material such as nylon, and are inserted at the ends of the housing units as shown in FIGURE 2 to prevent any detrimental friction or binding between the ends of rollers 14 in the end wall of the housing 16. Similarly, when more than one roller is employed in one housing, nylon inserts may be placed at the end of adjacent rollers to prevent binding between the rollers.

The amount of air pressure required will depend upon the size of rollers being employed, and must be suificient to lubricate the rollers 14 and also keep them away from 6 the internal wall portions of housing 16 during operation of the device.

Housing 16 has end walls so that the forced air entering therein from supply lines 18 can only escape around rollers 14. Care should be taken to ensure that the air supply entering housing 16 is clean, to avoid dirt particles or the like being blown onto the moving sheet material 10. The internal dimension of the housing must be such as to allow the roller to freely rotate therein with sufficient clearance to permit adequate air lubrication, of the rollers and eventual escape of the air.

The actual theory and mechanism of operation whereby the forced air maintains the rollers in yielding rotating contact with the sheet material but away from the housing walls has not been definitely ascertained. However, experiments have shown that the rollers will perform as aforesaid when suitable air pressure is emplyoed, but that the rollers will not operate effectively when no air pressure means is used.

Favourable operating results have been obtained in an apparatus similar to that shown in the attached drawings in connection with the detection of defects on coated paper employing 12 separate housing structures each containing one roller arranged across the sheet material 10, with the individual rollers 14 being formed of hardened and ground steel and being each 4" in length and A in diameter. Alternately, three housings containing four such rollers each have been found to give equally favourable results. The air pressure was constant at 7 psi. gauge, except of course when the device was not in operation whereupon the electromagnets 30 retained the rollers 14 within housings 16 which were made of Tobin bronze (a trademark representing a modified high strength brass of approximately 60% copper, 1% tin, traces of lead and iron, and the balance zinc). The speed of sheet material was approximately 600' per minute which meant that the rollers 14 were rotating at approximately 9,000 rpm.

The exact shape of housing 16 may of course be varied within the scope of the present invention, and may have outwardly curved walls, for example, designed so that as roller 14 moves vertically upwardly it falls into a pocket formed near the roof of housing 16 thus causing variations in air pressure corresponding to areas of abruptly increased thickness in sheet material 10, and this may be used as an alternate secondary sensing means as mentioned aforesaid. The bottom portion 27 of housing 16 may also be turned inwardly so as to prevent rollers 14 from falling out of housing 16 when the air is shut off, however care must be taken to ensure that such inturned portions do not interfere with the free rotation over moving sheet 10 or vertical movement of rollers 14.

The secondary sensing device may also utilize a variable capacitor as aforesaid as shown in FIGURE 5. Capacitor plates 42, 43 are provided in each side of inverted U- shaped housing 16, the plates being separated from each other and imbedded in an insulating material. The insulating material, together with the air space within the housing, acts as the dielectric material of the capacitor. The plates 42, 43 are simply arranged in an electrical circuit. Variation in the capacitance due to motion of the roller within the air gap causes a change in the capacitance of the electrical circuit.

The detecting device may also be arranged relative to roller 12 in positions other than as shown in the attached drawings. For example, if rollers 14 and housing 16 were positioned beneath sheet 10 so that the rollers 14 were normally urged upwardly by air pressure against the under side of sheet 10, it would not be necessary to employ electromagnets 30 since rollers 14 would remain within housing 16 by means of gravity when the air was shut off.

The detecting device of the invention may be employed in asssociation with paper or other sheet material machines of the type which cut preformed rolls of paper into the required dimensions as indicated hereinabove, or may be employed directly on paper making machines, or on separate testing machines. It will be understood that the invention may also be usefully applied to sheet material such as metal sheet, synthetic or plastic sheets or film and the like, as well as all type of paper for example, newsprint, tissue, fine and specialty papers and particularly coated paper where a smooth blemish-free surface is required.

Although the present invention has been described mainly by reference to specific preferred embodiments thereof, many modifications and variations may be made without departing from the spirit and scope of the invention as defined in the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A device for detecting areas of abruptly increased thickness on a web of moving sheet material comprising an unmounted roller arranged within a housing and free- 1y rotatable by said moving sheet material, air pressure means adapted to urge said roller into rotating yielding contact with the moving sheet material, and secondary sensing means which is actuated when said roller contacts an area of abruptly increased thickness on said sheet material.

2. A device for detecting areas of abruptly increased thickness on a web of moving sheet material comprising at least one unmounted roller freely rotatable by said moving sheet material and arranged within a housing, air pressure means adapted to urge said roller into rotating yielding contact with the moving sheet material and away from contact with the housing, secondary sensing means which is actuated when said roller contacts an area of abruptly increased thickness on said sheet material, and alarm means adapted to receive a signal from said actuated secondary sensing means.

3. A device for detecting areas of abruptly increased thickness on a web of moving sheet material comprising a plurality of unmounted rollers freely rotatable by said moving sheet material and arranged across said sheet material within inverted U-shaped housings secured above said moving sheet material, air pressure means forcing air into said housings and urging said rollers in rotating yielding contact with said moving sheet material and away from the wall of the housings, at least one of said rollers being vertically movable upon contacting an area of abruptly increased thickness on said sheet material, secondary sensing means dependent upon the relative position of said rollers and housings adapted to be actuated and to transmit a signal when one or more of said rollers moves vertically towards said housing away from said sheet material upon contacting an area of abruptly increased thickness on said sheet material, and alarm means adapted to receive signals from said secondary sensing means and to indicate those portions of the moving sheet material having undesirable areas of abruptly increased thickness.

4. A device according to claim 3 including retaining means adapted to hold the rollers away from the sheet material when the device is not in operation.

5. A device according to claim 3 wherein said secondary sensing means includes light transmitting means arranged on one side of the roller directed towards the point of contact of sheet material and roller and a photo electric cell arranged on the other side of said roller adapted to receive light from said light means when said roller moves away from said moving sheet material due to an area of abruptly increased thickness.

6. A device according to claim 3 wherein said secondary sensing means comprises an electrical capacitor system wherein at least part of said housing forms at least one plate of the capacitor and wherein said roller is adapted to displace part of the dielectric material of the capacitor thus varying the capacitance thereof and causing a signal to be transmitted to said alarm means.

7. A device according to claim 3 wherein said secondary sensing means comprises an electrical capacitor system, said housings being an inverted U-shape and containing a capacitor plate in each housing side wall, the air space within the housing between said side walls comprising at least part of the dielectric material of the capacitor, said roller being adapted to move further into said housing and into said air space upon contacting an area of abruptly increased thickness on said sheet material thus varying the capacitance of the capacitor and causing a signal to be transmitted to said alarm means.

8. A device according to claim 3 wherein said sheetmaterial is paper.

9. A device for detecting areas of abruptly increased thickness on a web of moving paper material comprising a plurality of rollers freely rotatable by said paper maare secured above said moving paper material, air pressure means forcing air downwardly through the roof of said housings adapted to lubricate said rollers and to urge said rollers into rotating yielding contact with said moving paper material and away from contact with the walls of said housings, at least one of said rollers being vertically movable upon contacting an area of abruptly increased thickness on said paper material, light transmitting means arranged on one side of said rollers and directed towards the point of contact of said paper material and said rollers, and a photoelectric cell arranged on the other side of said rollers adapted to receive light from said light means when said roller moves away from said moving paper material due to an area of abruptly increased thickness, said photoelectric cell being adapted to transmit a signal to alarm means which will indicate those portions of the moving paper material having undesirable areas of abruptly increased thickness.

10. A device according to claim 9 including retaining means adapted to hold the rollers away from the sheet material when the device is not in operation.

11. A device according to claim 9 including safety spring means associated with said housings and allowing said housings and rollers to move away from moving sheet material containing an area of abnormally increased thickness.

12. A device according to claim 9 wherein a plurality of rollers are arranged within one housing.

13. A device according to claim 9 wherein said rollers have nylon end portions to prevent binding between adjacent rollers.

14. A device according to claim 10 wherein said retaining means comprises electromagnets arranged in the roof of said housings and is adapted to retain the rollers within the housings when the device is not in operation.

15. A device according to claim 15) wherein said retaining means comprises electromagnets arranged in the roof of said housings adapted to retain said rollers within said housings when the device is not in operation, and

including switch means adapted to simultaneously en ergize said electromagnets and terminate said air pressure when the operation of the device is to be stopped.

16. A device for detecting areas of abruptly increased thickness on a web of moving sheet material comprising an inverted U-shaped housing located above the moving sheet material, roller means comprising at least one cylindrical roller freely rotatable by said sheet material and disposed across the moving sheet material between walls of said housing, said Ushaped housing being disposed such that the legs of the U are disposed across the moving sheet material and constitute walls thereof between which said roller is disposed, air pressure means to supply air to said housing means to bias said roller downwardly into rotating yielding contact with said moving sheet material, said roller being freely movable vertically between the walls of said housing and being spaced from the Walls thereof such that air supplied to said housing means to bias said roller downwardly flows between said roller and said Walls to lubricate same, whereby said roller is movable vertically relatively into said housing upon contacting an area of abruptly increased thickness on said sheet material.

17. A device according to claim 16 further including secondary sensing means comprising light transmitting means arranged on one side of said roller means directed toward the point of contact between said rollers and the sheet material and photoelectric cell means arranged on 15 1 0 References Cited UNITED STATES PATENTS 5/ 1923 Butterfield 33-447 6/1934 Nichols 33147 12/1934 Kronenberg 33147 8/1936 Hunt 33172 9/1941 Poock et a1 33172 4/1946 Agnew et a1. 33147 3/1959 Donaldson 33-147 9/1963 Nash 250219 FOREIGN PATENTS 1/1944 France. 1/ 1964 Great Britian.

LEONARD FORMAN, Primary Examiner.

ROBERT B. HULL, Examiner.

W. D. MARTIN, Assistant Examiner. 

1. A DEVICE FOR DETECTING AREAS OF ABRUPTLY INCREASED THICKNESS ON A WEB OF MOVING SHEET MATERIAL COMPRISING AN UNMOUNTED ROLLER ARRANGED WITHIN A HOUSING AND FREELY ROTATABLY BY SAID MOVING SHEET MATERIAL, AIR PRESSURE MEANS ADAPTED TO URGE SAID ROLLER INTO ROTATING YIELDING CONTACT WITH THE MOVING SHEET MATERIAL, AND SECONDARY SENSING MEANS WHICH IS ACTUATED WHEN SAID ROLLER CONTACTS AN AREA OF ABRUPTLY INCREASED THICKNESS ON SAID SHEET MATERIAL. 